revealingheart writes: ScienceDaily reports that on 5 and 6 June this year, millions of people around the world will be able to see Venus pass across the face of the Sun in what will be a once-in-a-lifetime experience. It will take Venus about six hours to complete its transit, appearing as a small black dot on the Sun's surface, in an event that will not happen again until 2117.

Transits of Venus occur only on the very rare occasions when Venus and Earth are in a line with the Sun. At other times Venus passes below or above the Sun because the two orbits are at a slight angle to each other. Transits occur in pairs separated by eight years, with the gap between pairs of transits alternating between 105.5 and 121.5 years — the last transit was in 2004.

"We are fortunate in that we are truly living in a golden period of planetary transits and it is one of which I hope astronomers can take full advantage," writes Jay M Pasachoff, an astronomer at Williams College, Massachusetts.